The invention concerns The refractory nozzle for arrangement in the wall of metallurgic vessels, especially for steel melts, comprising a passage opening having an upper and a bottom end, an inside wall of a solid electrolyte material enclosing the sides of the passageway opening. The nozzle has at least one electrode having connecting lines arranged electro-conductively at the outer side of the solid electrolyte material facing away from the passage opening, and has a thermally insulating material at least partially enclosing the outer side of the solid electrolyte material and the electrode.
Such a nozzle is known from U.S. Pat. No. 4,850,572. This patent describes an electrochemical method to prevent the deposition on the surface of the inside wall of the nozzle of material flowing through the nozzle.
From Japanese published patent application (kokai) JP 62-104655 A another nozzle arrangement is known, wherein the inner wall of the passage opening comprises a solid electrolyte layer, which is contacted by an outer electrode made of graphite. This is surrounded by an insulating material. A similar nozzle is known from Japanese published patent application (kokai) JP 57-85659 A.
Furthermore, it is known to heat refractory nozzles for molten metal. In U.S. Pat. No. 3,722,821 it is disclosed that a resistance heater is arranged around the inner wall of a nozzle with the purpose to counteract thermo-mechanical tensions and to prevent the solidification on the walls of the nozzle of material flowing through.
It is an object of this invention to make The refractory nozzle that is an improvement over known solutions and provides a highly reliable nozzle.
According to the invention, this object is achieved by having the at least one electrode made essentially of a metal and/or of an oxide thereof and having a melting point of at least about 1400xc2x0 C. Such electrodes are stable, so that a nozzle with such an arrangement is very reliable, stable and low cost. It is especially advantageous if the at least one electrode is made substantially from steel, chromium or Cr2O.
It is advantageous to have a chromium layer at least partially arranged in between the solid electrolyte material and the electrode, wherein this layer preferably has a thickness of approximately 50 xcexcm. One oxide of the metal of the electrode should have a conductivity of at least about 10xe2x88x922 xcexa9xe2x88x921 cmxe2x88x921 at a temperature of about 1400xc2x0 C. It is difficult to use the known copper electrodes to contact the appropriate solid electrolyte material, and the known graphite electrode material is easily oxidized to carbon monoxide or carbon dioxide, which could result in deterioration of the nozzle. Moreover, this problem is solved by the use of chromium, because the oxidation of this material is harmless, and Cr2O3 is also electrically conductive. The arrangement has a low electrical resistance over a long period of time. Cr2O3 can also be mixed with zirconia.
It is also useful to have a metal inlay, especially a wire mesh, arranged on the side of the electrode facing away from the solid electrolyte material. It is preferred that at least two electrodes be provided one after the other in axial direction of the passage opening and that the electrodes surround the solid electrolyte material in annular, tubular or spiral form. It is another advantage to have an electrically insulating material arranged between the ends of the passage opening and the at least one electrode. The insulating material of the refractory nozzle can be, for example, one or more materials selected from the group consisting of alumina, zirconia and mullite, particularly zirconia mullite having approximately 37 weight % zirconia and 63 weight % mullite.
The insulating material is bordered at its upper end by a preferably sintered ring of zirconia mullite, which encloses the solid electrolyte material. The ring of zirconia mullite can be arranged at the top end of the passage opening, and a cement can be arranged between the ring of zirconia mullite and the solid electrolyte material. The cement can be based on aluminum oxide, for example. It is advantageous to use a cement with a higher heat expansion coefficient than the ring of zirconia mullite and/or the solid electrolyte material, in order to create a tension in the direction of the center of the nozzle during the heating, and thus improve the strength of the device. In this case, the cement acts as a fastener ring that increases the strength of the device.
It is advantageous to have a heater, preferably a resistance heater, at least partially surrounding the outside of the solid electrolyte material, and enclosing the electrodes. The heater enables the preheating of the nozzle, to prevent tensions and deterioration of the material because of rapid temperature change. The heater is preferably formed in an annular, tubular or spiral manner on the outside of the solid electrolyte material, preferably within the thermal insulation material. The heater can be made of carbon or graphite; from a high melting point metal, especially molybdenum; from a carbide, especially silicon carbide; or from an oxide, especially Cr2O3. Zirconia is preferably used as a solid electrolyte material. It is of advantage that this solid electrolyte material of the inner wall have a density of more than about 5.2 g/cm3, a silica content of less than about 1.5 weight %, and that it preferably be sintered.